
difference(){
    union(){
difference(){
cylinder(h=15,r1=16,r2=16,$fn=100);
 cylinder(h=15,r1=15,r2=15,$fn=100);}
 difference(){
 cylinder(h=5,r1=15,r2=15,$fn=100);
  translate([0,0,1]){       
 cylinder(h=4,r1=4,r2=14.5,$fn=100);}}}


 for(i = [0 : 36: 360]){
 rotate([0,0,i]){
    cube([1,30,2]);}}}
 
 
 
 

rotate_extrude(convexity = 10, $fn = 100)
translate([20,0,0 ]){
    difference(){
circle(r = 1, $fn = 100);
circle(r = 0.5, $fn = 100);
    }
    }

translate([0,0,-0.5]){
cylinder(h=0.5,r1=20,r2=20,$fn=100);}